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From: Ian Collins <ian-news@hotmail.com>
Newsgroups: comp.lang.c++
Subject: Re: Length of C++ arrays allocated by operator new[]
Date: Mon, 22 Aug 2011 09:08:12 +1200
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On 08/22/11 08:39 AM, Marcel Müller wrote:
> On 20.08.11 18.36, Leigh Johnston wrote:
>> On 20/08/2011 17:26, A wrote:
>>>> SomeClass* array = new SomeClass[10];
>>>>
>>>> size_t length = get_length_of_array(array); // Impossible
>>>
>>> any particular reason you don't want to use vector instead and then use
>>> vect::size ?
>
> - The old platform does not support STL well.
> - STL causes the executable size to explode.

Only if you have a very poor linker.

> One disadvantage of
> template meta programming over generics. (Of course, there are many
> advantages on the other side.)

Who mentioned template meta-programming?

>> Yes, well said. std::vector should be preferred over dynamic arrays for
>> most cases;
>
> std::vector has the major disadvantage that any piece of code that has
> write access to its elements can also change its size and, more
> importantly, cause reallocations. That's sometimes not wanted and could
> cause hard to find bugs with UB, especially if the array is shared
> between threads.

Then derived privately and only expose a subset of members.  Or simply 
write your own array class.  Either way, the "avoid naked arrays" rule 
of thumb is still valid.

>> about the only case where one still needs to use dynamic
>> arrays is if you want to allocate but not initialize a buffer.
>
> Why? vector will always initialize /less/ or same than operator new[].
> The allocation size of the vector may be larger than logical size,
> containing additional uninitialized storage. new[] in contrast always
> invokes the standard constructors (if any).

So does vector's sized constructor.

-- 
Ian Collins